Dottorato in INGEGNERIA AERONAUTICA E SPAZIALE

Titolo della tesi: Multi-disciplinary design and multi-objective optimization of solid- and liquid- rocket based launch vehicles

Nowadays there is a tremendous competitiveness in the space sector, especially in the production of new launch vehicles. Launch Vehicle design is a complex topic, because it requires the knowledge of different disciplines such as propulsion, structures, aerodynamics, trajectory and controls, which are strongly coupled between each others. Therefore, Multidisciplinary Design Optimization is the correct approach to study and develop new launch vehicle configurations. Each discipline requires the adoption of a proper engineering model to accurately describe its physic. Many researches have been carried out on launch vehicle design optimization. However, the exploitation of finite element model and computational fluid dynamics inside an optimization loop is still not common due to the huge computational time required to perform a structural and an aerodynamic analysis. This thesis proposes a methodology for a fast and effective multidisciplinary design optimization using a high fidelity structural model generator, surrogate and reduced order models to accelerate the phase A of development of new launch vehicles, balancing accuracy and computational time. Indeed, the use of finite element surrogate models together with the real finite element solver enhances the process of identifying the optimal design by enabling reduction in the running time of the optimization procedure, making the finite element analysis suited for conceptual studies. While, the use of a reduce order model for aerodynamic permits to complete avoid computational fluid dynamics calculation inside the optimization loop. More specifically, it is developed a procedure which, starting by a target payload and mission, calculates the optimal propellant distribution between the stages in order to minimize the launch vehicle mass. Then, once defined the mass budget and the external geometry, the trajectory up to target orbit is evaluated and consequently the flight loads necessary to carry out the structural analysis using both a refined finite element model and its surrogate. The multidisciplinary design optimization procedure is managed in an advanced optimization environment in order to find the best values of design variables that minimize or maximize the cost functions while respecting the mission constraints. In order to validate this methodology, two launch vehicle configurations have been studied: a three stages solid- and a two stages liquid- rocket based launch vehicle. On the three stages configuration have been firstly carried out a structural optimization and after the complete multidisciplinary optimization considering single and multiple objectives. Instead on the two stages has been performed a complete multidisciplinary design optimization cycle with two separated objectives.